Method of making diamond product and diamond product

ABSTRACT

The method of making a diamond product in accordance with the present invention comprises the steps of forming a diamond substrate ( 50 ) with a mask layer ( 52 ), and etching the diamond substrate ( 50 ) formed with the mask layer ( 52 ) with a plasma of a mixed gas composed of a gas containing an oxygen atom and a gas containing a fluorine atom, whereas the fluorine atom concentration is within the range of 0.04% to 6% with respect to the total number of atoms in the mixed gas.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method of making a diamond product byetching, and the diamond product.

2. Related Background Art

Plasma etching, which can remove a large amount of diamond at once andcan be carried out relatively easily, has been utilized as a techniquefor processing diamond. Usually, oxygen gas is used for plasma etchingof diamond. Etching with oxygen alone, however, has formed a largenumber of unnecessary acicular protrusions on the surface of theresulting diamond product, thus failing to smooth the surface.Therefore, attention has been given to a technique in which other gasesare introduced into a reaction chamber together with oxygen gas so as toflatten the diamond surface. For example, Hiroshi Shiomi, New Diamond,Vol. 13, No. 4, p. 28 (1997) discloses a technique in which diamond isetched with a plasma of a mixed gas composed of oxygen gas and CF₄ gas.This etching technique enables the plasma of CF₄ gas to remove theunnecessary acicular protrusions and flatten the surface of diamondproduct.

SUMMARY OF THE INVENTION

However, the technique disclosed in the above-mentioned publication hasthe following problem. Namely, when a diamond substrate 102 is etched byway of a mask 104 as shown in FIG. 14A, thus etched side faces 102S maynot become perpendicular but tilt greatly as shown in FIG. 14B, thusyielding a trapezoidal cross section.

In order to overcome the above-mentioned problem, it is an object of thepresent invention to provide a method of making a diamond product, whichcan fully flatten the surface of diamond product and make its etchedside faces substantially perpendicular; and such a diamond product.

The inventors carried out diligent studies and, as a result, have foundthat the above-mentioned object can be achieved by the followinginvention.

Namely, the present invention provides a method of making a diamondproduct by etching, the method comprising the steps of forming a diamondsubstrate with a mask layer; and etching the diamond substrate formedwith the mask layer with a plasma of a mixed gas composed of a gascontaining an oxygen atom and a gas containing a fluorine atom; whereinthe fluorine atom has a concentration within the range of 0.04% to 6%with respect to the total number of atoms in the mixed gas.

The inventors have found that, though the unnecessary protrusions can beeliminated when the fluorine concentration in the etching gas is raised,the mask layer is laterally shaved with fluorine when its concentrationis too high, so that the etched side faces may incline. In recognitionof this fact, the inventors have found that, when the fluorine atomconcentration is lowered so as to fall within the above-mentioned range,the mask layer is restrained from being shaved laterally, whereby theetched side faces can be made substantially perpendicular; and that,even when the fluorine atom concentration is lowered so as to fallwithin the above-mentioned range, the number of unnecessary protrusionsis sufficiently reduced, whereby the etched surface of diamond productis flattened.

Preferably, in the method of making a diamond product in accordance withthe present invention, the plasma is produced by generating ahigh-frequency discharge between two plate electrodes arranged inparallel, whereas the high-frequency discharge is generated by supplyingan electric power of at least 0.45 W/cm² between the plate electrodes.

When the output for generating the high-frequency discharge is enhancedas such, it becomes easier for the fluorine atom to attain a plasmastate, whereby the number of unnecessary protrusions can sufficiently bereduced even when the amount of fluorine is small.

Preferably, in the method of making a diamond product in accordance withthe present invention, the gas containing the fluorine atom is CF₄ gas,whereas the CF₄ gas has a concentration within the range of 0.02% to 3%with respect to the total number of molecules in the mixed gas.

When CF₄ gas, which is safe and easy to use, is employed, an etchingprocess for the diamond substrate can be carried out smoothly.

Preferably, in the method of making a diamond product in accordance withthe present invention, the gas containing the oxygen atom is one of O₂,CO₂, and a mixed gas composed of O₂ and CO₂.

The diamond product in accordance with one aspect of the presentinvention comprises a diamond substrate; a plurality of alignedprotrusions made of diamond, formed on the diamond substrate by etching,and arranged according to a predetermined rule; and a plurality ofsubsidiary protrusions randomly formed between the plurality of alignedprotrusions upon etching; wherein the aligned protrusions have a sideface with an angle of inclination of at least 78°, whereas thesubsidiary protrusions have a top part which is not flat, and the numberof the subsidiary protrusions is not greater than 20 per 25 μm².

Among diamond products in which a plurality of protrusions are formed byetching, those having such a small number of subsidiary protrusions withtheir aligned protrusions having side faces with an angle of inclinationof at least 78° have not conventionally existed. For example, theabove-mentioned manufacturing method of the present invention can make adiamond product having a flat surface with aligned protrusions havingsubstantially perpendicular side faces as such. The portion of diamondsubstrate covered with the mask layer can attain a flat top part whenthe mask layer is removed. However, the subsidiary protrusions areformed in a portion not covered with the mask, whereby their top part isnot flat. Here, the condition that the number of the subsidiaryprotrusions is not greater than 20 per 25 μm² also encompasses the casewhere there is no subsidiary protrusion.

The diamond product in accordance with another aspect of the presentinvention comprises a diamond substrate having a recess formed byetching; and a plurality of subsidiary protrusions randomly formed at abottom part of the recess upon etching; wherein the recess has a sideface with an angle of inclination of at least 78°, whereas thesubsidiary protrusions have a top part which is not flat, and the numberof the subsidiary protrusions is not greater than 20 per 25 μm².

Among diamond products in which a recess is formed by etching, thosehaving such a small number of subsidiary protrusions with their recesshaving a side face with an angle of inclination of at least 78° have notconventionally existed. The above-mentioned manufacturing method of thepresent invention can make a diamond product having a flat surface(bottom part of the recess) with the recess having a substantiallyperpendicular side face as such. Here, the condition that the number ofthe subsidiary protrusions is not greater than 20 per 25 μm² alsoencompasses the case where there is no subsidiary protrusion.

The diamond product in accordance with another aspect of the presentinvention comprises a diamond substrate; one protrusion made of diamondand formed on the diamond substrate by etching; and a plurality ofsubsidiary protrusions randomly formed about the one protrusion uponetching; wherein the one protrusion has a side face with an angle ofinclination of at least 78°, whereas the subsidiary protrusions have atop part which is not flat, and the number of the subsidiary protrusionsis not greater than 20 per 25 μm².

Among diamond products in which one protrusion is formed by etching,those having such a small number of subsidiary protrusions with the oneprotrusion having a side face with an angle of inclination of at least78° have not conventionally existed. The above-mentioned manufacturingmethod of the present invention can make a diamond product having a flatsurface with the one protrusion having substantially perpendicular sidefaces as such. The portion of diamond substrate covered with the masklayer can attain a flat top part when the mask layer is removed.However, the subsidiary protrusions are formed in a portion not coveredwith the mask, whereby their top part is not flat. Here, the conditionthat the number of the subsidiary protrusions is not greater than 20 per25 μm² also encompasses the case where there is no subsidiaryprotrusion.

The method of making a diamond product in accordance with another aspectof the present invention is a method of making a diamond product byetching, the method comprising the steps of forming a diamond substratewith a mask layer; and etching the diamond substrate formed with themask layer with a plasma of a mixed gas composed of a gas containing anoxygen atom and a gas containing a halogen atom; wherein, in an emissionspectrum of the mixed gas, an intensity A of an emission peak caused bythe oxygen atom and an intensity B of an emission peak caused by oxygenhave an intensity ratio A/B which is greater than the intensity ratioA/B obtained from an emission of a plasma which is 100% oxygen.

The greater the intensity ratio A/B is, the greater becomes the ratio ofoxygen atom (O) to oxygen (O₂). The oxygen atom is easier to etchdiamond than is the oxygen molecule, thus improving the etching speed.Also, the mask layer is formed with a firm oxide film as the oxygen atomconcentration increases. Therefore, the mask layer is restrained frombeing shaved laterally, whereby the etched side faces can be madesubstantially perpendicular. Further, the halogen atom can remove theunnecessary protrusions formed upon etching.

Preferably, the gas containing the halogen atom in the above-mentionedmixed gas is CF₄, and the mixed gas further contains nitrogen gas. Theinventors have found that, when the mixed gas is composed as such, theintensity ratio A/B improves, thereby enhancing the diamond etchingspeed.

Also, the emission peak caused by the oxygen atom may have a half widthof 3 nm or less, whereas the emission peak caused by oxygen may have ahalf width greater than 3 nm.

The present invention will become more fully understood from thedetailed description given hereinbelow and the accompanying drawingswhich are given by way of illustration only, and thus are not to beconsidered as limiting the present invention.

Further scope of applicability of the present invention will becomeapparent from the detailed description given hereinafter. However, itshould be understood that the detailed description and specificexamples, while indicating preferred embodiments of the invention, aregiven by way of illustration only, since various changes andmodifications within the spirit and scope of the invention will becomeapparent to those skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing an etching apparatus for making adiamond product;

FIGS. 2A to 2C are flowcharts showing a first embodiment of the methodof making a diamond product in accordance with the present invention;

FIGS. 3A to 3C are flowcharts showing a second embodiment of the methodof making a diamond product in accordance with the present invention;

FIG. 4 is a graph showing emission peaks utilized in a third embodimentof the method of making a diamond product in accordance with the presentinvention;

FIG. 5 is a graph showing relationships between the CF₄ gasconcentration and the emission intensity ratio A/B;

FIG. 6 is a graph showing relationships between the N₂ gas concentrationand the emission intensity ratio A/B;

FIG. 7 is an electron micrograph showing a diamond product obtained bythe method of the third embodiment;

FIG. 8 is an electron micrograph showing a diamond product obtained bythe method of the third embodiment;

FIG. 9 is an electron micrograph showing a diamond product obtained bythe method of the third embodiment;

FIG. 10 is a chart showing etching conditions of Examples andComparative Examples;

FIG. 11 is a chart showing results of experiments of Examples andComparative Examples;

FIG. 12 is a photograph showing the diamond product obtained by Example3;

FIG. 13 is a photograph showing the diamond product obtained by Example4; and

FIGS. 14A and 14B are views employed for explaining a conventionalmethod of making a diamond product.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following, preferred embodiments of the method of making adiamond product and the diamond product in accordance with the presentinvention will be explained in detail with reference to the accompanyingdrawings. Here, constituents identical to each other will be referred towith numerals identical to each other without repeating theiroverlapping explanations.

First Embodiment

FIG. 1 is a schematic diagram showing the etching apparatus employed inthe first embodiment. This etching apparatus 1 comprises an etchingchamber 10 for subjecting a diamond substrate 50 to RIE (Reactive IonEtching), and an introduction chamber 20 communicating therewith by wayof a gate valve 14 adapted to open and close. The introduction chamber20 is a space for introducing the diamond substrate 50 into the etchingchamber 10 and is provided in order that the etching chamber 10 caneasily attain a vacuum state therein. Also, the etching apparatus 1 isconfigured such that a substrate carrier member 24 can be introducedtherein from the left side in the drawing by opening a lid of theintroduction chamber 20, which is not depicted. The front end part ofthe substrate carrier member 24 is equipped with a substrate holder 22for holding the diamond substrate 50. By use of the substrate carriermember 24, the diamond substrate 50 set to the substrate holder 22 inthe outside of the etching apparatus 1 can be transported into theetching chamber 10.

The etching chamber 10 is provided with two lines of gas introductionunits 14, 16 each constituted by valves and a mass flow controller. Thegas introduction unit 14 is used for introducing O₂ gas into the etchingchamber 10, whereas the gas introduction unit 16 is used for introducingCF₄ gas (a gas containing fluorine) into the etching chamber 10. Namely,this embodiment utilizes a mixed gas composed Of O₂ gas and CF₄ gas.Though the gas containing fluorine is not limited to CF₄ gas, theetching process for the diamond substrate 50 can be carried out smoothlyby using CF₄ gas, which is safe and easy to use.

The concentration of CF₄ gas with respect to the total number of atomsin the mixed gas is set so as to fall within the range of 0.04% to 6% inthe etching chamber 10. Namely, in this embodiment, the concentration ofCF₄ gas with respect to the total number of atoms in the mixed gas isset so as to fall within the range of 0.02% to 3%. In place of O₂ gas, agas containing an oxygen atom such as CO₂ gas or a mixed gas composed ofO₂ and CO₂ may also be used.

Within the etching chamber 10, two plate electrodes 18, 19 are arrangedface-to-face in parallel. At the time of etching, the diamond substrate50 is mounted on the plate electrode 18. The plate electrodes 18, 19 areconnected to a high-frequency power source (RF power source) 17. Whenelectric power is supplied between the plate electrodes 18, 19 from thehigh-frequency power source 17, a discharge occurs between the plateelectrodes 18, 19, whereby the mixed gas composed of O₂ gas and CF₄ gascan attain a plasma state. Also, when a voltage is applied between theplate electrodes 18, 19, a negative bias is imparted to the plateelectrode 18 due to the plasma potential.

Connected to the etching chamber 10 and introduction chamber 20 is aconversion mechanism 40 for yielding a vacuum state therein andcanceling the vacuum state by introducing N₂ gas therein. The conversionmechanism 40 has a turbo pump 42 and a rotary pump 44 on the etchingchamber 10 side, and a turbo pump 43 and a rotary pump 45 on theintroduction chamber 20 side. When these pumps 42 to 45 are actuated, avacuum state can be attained within the etching chamber 10 andintroduction chamber 20. On the other hand, a gas introduction pipe 46for introducing N₂ gas is connected to the etching chamber 10 andintroduction chamber 20. When N₂ gas is introduced into the etchingchamber 10 and introduction chamber 20 in the vacuum state through thegas introduction pipe 46, lids of the etching chamber 10 andintroduction chamber 20 can be opened, so as to let out or let indiamond substrate 50.

The method of making a diamond product in accordance with thisembodiment, and the diamond product obtained thereby will now beexplained with reference to FIGS. 1 and 2A to 2C.

First, as shown in FIG. 2A, the diamond substrate 50 is formed with masklayers 52 made of Al by a photolithography technique. The diamondsubstrate 50 may be any of single-crystal substrates, hetero-epitaxialsubstrates, and polycrystal substrates. A plurality of mask layers 52,each having a circular form, are formed into a matrix. Namely, the masklayers 52 are arranged according to a matrix rule. Subsequently, thediamond substrate 50 is set to the substrate holder 22 of the substratecarrier member 24, and put into the introduction chamber 20 of theetching chamber 1. Then, the pumps 42 to 45 are actuated so as to yielda vacuum state in the etching chamber 10 and introduction chamber 20.Thereafter, the gate valve 12 is opened, and the diamond substrate 50 ismounted on the plate electrode 18. After the substrate carrier member 24is drawn out of the etching chamber 10, the gate valve 12 is closed.

After the foregoing preparation, O₂ gas and CF₄ gas are introduced intothe etching chamber 10 from the gas introduction units 14 and 16,respectively. Subsequently, the high-frequency power source 17 isactuated, so as to generate a high-frequency discharge between the plateelectrodes 18, 19. Here, it is preferred that the high-frequency powersource 17 supply an electric power of at least 0.45 W/cm² between thetwo plate electrodes 18, 19. When a discharge occurs between the plateelectrodes 18, 19, the mixed gas composed of O₂ gas and CF₄ gas isexcited, so as to attain a plasma state.

The O₂ gas and CF₄ gas in the plasma state are attracted toward theplate electrode 18, whereby the diamond substrate 50 is etched. FIG. 2Bis a sectional view showing a diamond product 60 formed by etching thediamond substrate 50. FIG. 2C is a plan view showing the diamond product60 in a state where the mask layers 52 are removed.

As can be seen from FIGS. 2B and 2C, the diamond product 60 inaccordance with this embodiment formed by etching has a structure inwhich a plurality of aligned protrusions 62 formed in conformity to thepositions and forms of the respective mask layers 52 are integrated onthe diamond substrate 50, whereas a plurality of subsidiary protrusions72 which are inherently unnecessary are formed among the alignedprotrusions 62.

Since a plurality of aligned protrusions 62 are formed in conformity tothe respective mask layers 52, they are arranged according to a matrixrule as shown in FIG. 2C. Also, each of the aligned protrusions 62 isutilizable as an emitter for an electron emission device, a rotary shaftor gear for a micro machine, an optical component such as a diffractiongrating, diffraction lens, prism, or photonic crystal, a proberonanatomic level (AFM/STM, optical prober, or the like), a mold for aresin or other materials, a marker for inscribing letters or symbols,and the like. Its side face 62S has an angle of inclination α of atleast 78°. The angle of inclination of the aligned protrusions 62 thusbecomes large and substantially perpendicular due to the followingreason. Namely, the mask layers 52 can be restrained from being shavedlaterally at the time of etching when the fluorine concentration withrespect to the total number of atoms of the mixed gas in the etchingchamber 10 is lowered so as to fall within the range of 0.04% to 6%,i.e., the CF₄ gas concentration with respect to the total number ofmolecules is lowered so as to fall within the range of 0.02% to 3%.

A plurality of subsidiary protrusions 72 are randomly formed uponetching at positions not intended by the manufacturer of the diamondproduct 60, and are unnecessary since they do not function at all whenthe diamond product 60 is used for electron emission devices and thelike. A greater number of such subsidiary protrusions 72 can be removedas the amount of fluorine content in the etching gas is larger. In thisembodiment, the number of such subsidiary protrusions 72 is small, i.e.,20 or less per 25 μm². Such a small number of subsidiary protrusions 72hardly affect the quality of the electron emission device or the likewhen the diamond product 60 is used therefor. Namely, even when thefluorine concentration in the mixed gas is lowered to theabove-mentioned range, the number of subsidiary protrusions 72 can bereduced to a permissible density. The condition that the number of thesubsidiary protrusions 72 is 20 or less encompasses the case where thereis no subsidiary protrusion 72.

The top part of such a subsidiary protrusion 72 is often formed acicular without being flattened. This is because of the fact that,though the aligned protrusions 62 have a flat top part since they areformed in the portion of diamond substrate 50 covered with the masklayers 52, the subsidiary protrusions 72 are formed in the portion ofdiamond substrate 50 not covered with the mask layers 52.

In this embodiment, the high-frequency power source 17 supplies a highelectric power of at least 0.45 W/cm² between the plate electrodes 18,19, so that the fluorine atom is likely to attain a plasma state,whereby the number of subsidiary protrusions 72 can be made sufficientlysmall even if the amount of fluorine is small.

Also, since the fluorine concentration is lowered as mentioned abovewhile the concentration of oxygen contributing to etching diamond isenhanced, the etching speed can be increased in this embodiment.Therefore, the method of making a diamond product in accordance withthis embodiment is not only utilizable as a process for making anelectronic device, but also usable in place of the machining or laserprocessing for grinding or cutting diamond.

When the method of this embodiment is used in place of machining, theprocess can be done in a shorter period of time as compared withmachining, and there is no fear of the diamond substrate breaking due tothe pressure occurring at the time of machining. While the machiningcannot partly remove the diamond substrate by using a mask, it can beachieved in this embodiment.

While the laser processing requires a cutting margin of about 20 μm toabout 40 μm when cutting a diamond substrate having a thickness of 100μm, for example, the cutting margin can be reduced to about 5 μm or lessby the method of this embodiment in which etched side faces becomesubstantially perpendicular. Therefore, a greater number of protrusionsand depressions can be formed in the same substrate. In the laserprocessing, on the other hand, a graphite layer, which is anelectrically conductive layer, is formed on side faces, whereby the sidefaces have to be processed in diamond substrates which require electricinsulation. Such a process is not necessary in this embodiment. Further,the diamond substrate can be prevented from being damaged by the heat oflaser in this embodiment.

The method of this embodiment capable of perpendicular etching canincrease the height of aligned protrusions 62 or depth of depressions 76in the diamond product. Also, a large number of protrusions 62 ordepressions 76 can be formed with very small intervals. Therefore, thesurface area of diamond product drastically increases as compared withthat conventionally available. When the diamond product having thiseffect is utilized, chemical electrodes for detecting chemicalsubstances, sensor electrodes for detecting acids and alkalis, secondaryelectrodes, and the like can be manufactured with a small size, a highsensitivity, and a high performance.

Though the diamond substrate 50 is formed with a plurality of alignedprotrusions 62 in this embodiment, the diamond substrate may be formedwith only one diamond protrusion whose side face has an angle ofinclination of at least 78° by etching, whereas the number of subsidiaryprotrusions randomly formed about this protrusion is set to 20 or lessper 25 μm².

Second Embodiment

The second embodiment of the present invention will now be explainedwith reference to FIGS. 3A to 3C. First, as shown in FIG. 3A, a masklayer 53 made of Al is formed on a diamond substrate 50. A circularwindow 53 a is formed at the center part of the mask layer 53. When thediamond substrate 50 is etched in the same manner as in the firstembodiment, a diamond product 70 shown in FIG. 3B can be obtained. FIG.3C is a plan view of the diamond product 70 in the state where the masklayer 53 is removed.

As can be seen from FIGS. 3B and 3C, the diamond product 70 of thisembodiment formed by etching has a structure in which the diamondsubstrate 50 is formed with a depression (recess) 76. The depression 76is formed in conformity to the position and form of the window 53 a ofthe mask layer 53, and has a bottom face formed with a plurality ofsubsidiary protrusions 72 which are inherently unnecessary.

The depression 76 has a side face 76S whose angle of inclination β is atleast 78°. The angle of inclination β of the side face 76S becomesgreater as such due to the following reason. Namely, as in the firstembodiment, the mask layer 53 can be restrained from being shavedlaterally at the time of etching when the fluorine concentration withrespect to the total number of atoms of the mixed gas in the etchingchamber 10 is lowered so as to fall within the range of 0.04% to 6%,i.e., the CF₄ gas concentration with respect to the total number ofmolecules is lowered so as to fall within the range of 0.02% to 3%.

A plurality of subsidiary protrusions 72 are randomly formed uponetching at positions not intended by the manufacturer of the diamondproduct 70. A greater number of such subsidiary protrusions 72 can beremoved as the amount of fluorine content in the etching gas is larger.In this embodiment, the number of such subsidiary protrusions 72 issmall, i.e., 20 or less per 25 μm². Such a small number of subsidiaryprotrusions 72 hardly affect the quality of the diamond product 70 whenin use. Namely, even when the fluorine concentration in the mixed gas islowered to the above-mentioned range, the number of subsidiaryprotrusions 72 can be reduced to a permissible density.

The top part of such a subsidiary protrusion 72 is often formed acicular without being flattened. This is because of the fact that,though the portion covered with the mask layer 53 attains a flat toppart, the subsidiary protrusions 72 are formed in the portion of diamondsubstrate 50 not covered with the mask layer 53. The depression (recess)may have a multistage structure instead of the single-stage structure.

Third Embodiment

The third embodiment of the present invention will now be explained. Inthis embodiment, the gas employed for etching is a mixed gas composed ofa gas containing an oxygen atom and a gas containing a halogen atom,while the mixed gas attains a predetermined emission spectrum.Specifically, the mixed gas is subjected to spectrometry, so as toobtain an emission peak X caused by the oxygen atom (O) and an emissionpeak Y caused by oxygen (O₂). Employed for etching in this embodiment isa mixed gas in which the intensity A of emission peak X and theintensity of emission peak Y yield an intensity ratio A/B which isgreater than the intensity ratio A/B obtained from the emission of aplasma which is 100% oxygen.

For measuring the spectrum, known light sources, spectrometers,detectors, signal processors, and the like can be utilized. For example,an etching apparatus (RIE) formed with a window through which a plasmacan be observed from the outside is employed, and the emission generatedby the plasma is made incident on an external spectrometer by use of anoptical fiber or the like. Subsequently, its spectrum is acquired, andthe spectrum within the wavelength range of 400 nm to 900 nm isobserved. Here, it is preferred that not the sheath portion formed inthe plasma and substrate but the light-emitting portion be subjected tospectrometry.

FIG. 4 is a graph showing relationships between the emission wavelength(nm) of mixed gases and the emission intensity of the spectrum of mixedgases. Each mixed gas contained CF₄ as a gas containing a halogen atom,and O₂ as a gas containing an oxygen atom. The emission spectrum wasmeasured for each of three patterns of mixed gases in which the CF₄ gasand O₂ gas had different concentration ratios therebetween. For eachpattern of mixed gas, acute emission peaks X caused by the oxygen atomwere generated in the vicinity of 614 nm, 777 nm, and 844 nm, whereasemission peaks Y caused by oxygen, which were broader than the emissionpeaks X, were generated in the vicinity of 526 nm, 558 nm, 597 nm, 637nm, and 680 nm. Among them, the emission peak X in the vicinity of 777nm and the emission peak Y in the vicinity of 558 nm have such a highemission intensity that they are easily recognizable, whereby they areeasily utilized for calculating the intensity ratio A/B.

Here, each of the emission peaks X caused by the oxygen atom has a halfwidth of 3 nm or less, whereas each of the emission peaks Y caused byoxygen tends to become broader so as to have a half width greater than 3nm, whereby they are easily distinguishable from each other.

When a mixed gas defined as in this embodiment is utilized in themanufacturing method of the first or second embodiment, the followingeffect is obtained. As the intensity ratio A/B is greater, the ratio ofoxygen atom (O) to oxygen (O₂) becomes greater. Since the oxygen atometches diamond more easily than does the oxygen molecule, the etchingspeed improves. When the oxygen atom concentration is enhanced, the masklayer is formed with a firm oxide film. Therefore, the mask layer isrestrained from being shaved laterally, whereby etched side faces can bemade substantially perpendicular. Further, the halogen atom can removeunnecessary protrusions formed at the time of etching.

Due to the following reason, the intensity ratio A/B of etching gas iscompared with the intensity ratio A/B obtained from the emission of aplasma which is 100% oxygen. Namely, while the state of a plasma isinfluenced by various factors such as power, pressure, substratetemperature, and apparatus form, the intensity ratio A/B varies inrelation to these factors, whereby it can be considered as a referencevalue for the substantial effect alone. Specifically, for example, whenthe power is raised, the oxygen decomposing ratio rises, so that thevalue of intensity ratio A/B increases, thereby accelerating the diamondetching speed. However, it also yields a negative effect of increasingthe ion energy, so that the etching speed of the mask is improved aswell, whereby the aimed object cannot be achieved. Therefore, it will beappropriate if the intensity ratio A/B obtained from the emission of aplasma which is 100% oxygen is employed as a reference.

When the mixed gas containing CF₄ gas and O₂ gas further containsnitrogen gas, the intensity ratio A/B is improved, so that the diamondetching speed is enhanced.

Further, the gas containing a halogen atom in the mixed gas is notlimited to CF₄ and can utilize various substances such as chlorine,bromine, and iodine as long as it yields an intensity ratio A/B greaterthan the intensity ratio A/B obtained from the emission of a plasmawhich is 100% oxygen.

FIG. 5 is a graph showing intensity ratios A/B obtained from a pluralityof etching gases among which the concentration ratios of CF₄ gas variedwhile utilizing a mixed gas composed of CF₄ gas and O₂ gas as each ofthe etching gases. Each of peaks at wavelengths of 614 nm, 777 nm, and844 nm was used as the emission peak X, whereas the peak at a wavelengthof 558 nm was used as the emission peak Y, whereby the intensity ratioA/B was calculated. Though slight fluctuations were seen in the threemeasurement results among which the wavelength of emission peak Xvaried, similar tendencies were obtained.

In FIG. 5, each of the plots where the concentration of CF₄ gas is 0%indicates the intensity ratio A/B obtained from the emission of a plasmawhich is 100% oxygen. These plots are located on the leftmost side inthe graph. Mixed gases yielding an intensity ratio greater than theintensity ratio A/B of these plots correspond to the mixed gas in thisembodiment. The intensity ratios of individual plots were easilydistinguishable from each other in particular when the emission peak Xat a wavelength of 777 nm was utilized. Here, the intensity ratio A/Battained its maximum value when the CF₄ gas was 1% to 2% of the wholemixed gas, and yielded a value exceeding by about 0.05% to about 3% theintensity ratio A/B obtained from the emission of a plasma which was100% oxygen.

The effect obtained when the mixed gas further contains nitrogen gaswill now be explained with reference to FIG. 6. Here, the emissionintensity ratio was calculated for each of two kinds of mixed gases,i.e., a mixed gas composed of O₂ gas and N₂ gas, and a mixed gascomposed of O₂ gas, CF₄ gas, and N₂ gas. The latter mixed gas was dopedwith 1% of CF₄ gas.

When the gas containing no CF₄ gas, i.e., the gas containing no halogenatom, was caused to contain N₂ gas, the intensity ratio A/B did notattain a maximum value, thereby failing to yield a value exceeding theintensity ratio A/B caused by the emission of a plasma which was 100%oxygen as can be seen from FIG. 6. When the gas containing CF₄ gas wascaused to contain N₂ gas, by contrast, a maximum value was obtained atan appropriate value. These facts have revealed that desirable etchingin this embodiment cannot be realized when N₂ gas is simply added to O₂gas, but a diamond product having a substantially perpendicular sideface and a flat etching face can be obtained when N₂ gas is added to amixed gas containing O₂ gas and N₂ gas.

Also, as can be seen from the electron micrographs of FIGS. 7 to 9, adiamond product having very small protrusions can be formed when a masklayer having a very small area is utilized in the method of thisembodiment. These protrusions can be formed directly on the surface ofthe substrate as shown in FIG. 7, or formed at upper ends of relativelythick protrusions or bulges as shown in FIGS. 8 and 9. The protrusionsin FIG. 8 have substantially columnar forms, whereas those in FIG. 9 areformed conical. These protrusions can be utilized as pointed probes orpointed electron emitters.

EXAMPLES

The present invention will now be explained more specifically withreference to Examples.

Using a single-crystal diamond Ib(100) substrate as a diamond substrate,mask layers made of Al were formed into a matrix thereon. As the etchinggas, a mixed gas composed of O₂ gas and CF₄ gas was employed. Then,using the etching apparatus 1 shown in FIG. 1, experiments of Examples 1to 12 and Comparative Examples 1 to 3 were carried out.

FIG. 10 shows etching conditions of Examples and Comparative Examples,whereas FIG. 11 shows the results of experiments.

As can be seen from FIG. 10, diamond products having aligned protrusionswere formed while the CF₄ gas concentration (fluorine concentration)with respect to the total number of molecules in the mixed gas wasvaried among Examples 1 to 6 and Comparative Examples 1 to 3. InExamples 7 to 12, diamond products having aligned protrusions wereformed while the output value of high-frequency electric power forgenerating a plasma was varied under the condition where the CF₄ gasconcentration was held constant. Each of the flat electrodes in theetching chamber had an area of 177 cm².

As can be seen from FIG. 11, the surface state of diamond product, theetching speed of diamond substrate in the height direction, the etchingdepth (height of aligned protrusions), the angle of inclination of sidefaces of aligned protrusions, the etching speed of the mask layer in theheight direction, and the etching selection ratio (the ratio of theetching speed in the height direction of the mask layer to the etchingspeed in the height direction of the diamond substrate) were measured inthese experiments. As for the surface state of diamond product, the casewhere no subsidiary protrusion exists is indicated by a double circle,the case where the number of subsidiary protrusions is 20 or less per 25μm² is indicated by a single circle, and the case where the number ofsubsidiary protrusions exceeds 20 per 25 μm² is indicated by a cross.

When the CF₄ gas concentration with respect to the total number ofmolecules in the mixed gas fell within the range of 0.02% to 3% (thefluorine gas concentration with respect to the total number of atoms inthe mixed gas was 0.04% to 6%), as can be seen from Examples 1 to 6, itwas possible to form a diamond product having such a favorable surfacestate that subsidiary protrusions exist by only 20 or less per 25 μm² ifany, and aligned protrusions with side faces having an angle ofinclination α within the range of 88° to 90°.

FIG. 12 is a photograph showing the diamond product obtained in Example3 (where the concentration of CF₄ gas was 1%). As can be seen from thisphotograph, the diamond product was formed with a plurality of alignedprotrusions arranged in a matrix, whereas no subsidiary protrusionsexisted. The aligned protrusions exhibited a greater angle ofinclination α.

FIG. 13 is a photograph showing the diamond product obtained in Example4 (where the concentration of CF₄ gas was 0.1%). As can be seen fromthis photograph, the diamond product was formed with a plurality ofaligned protrusions arranged in a matrix, whereas subsidiary protrusionswere formed among the aligned protrusions. However, the number ofsubsidiary protrusions was so small that they did not affect the use ofthe diamond product. The side faces of aligned protrusions weresubstantially perpendicular.

When the concentration of CF₄ gas was increased to 5% as in ComparativeExample 1, the mask layers were laterally shaved during etching, so thatthe angle of inclination α was reduced to 72°. When the concentration ofCF₄ gas exceeded 5%, substantially all the mask layers were shaved,whereby it was impossible to form aligned protrusions.

When the CF₄ gas concentration was reduced to 0.01% or O₂ gas was usedalone as the etching gas without using CF₄ gas as in Comparative Example2 or 3, the number of subsidiary protrusions exceeded 20 per 25 μm²,whereby the surface state of the diamond product was rough.

In Examples 7 to 12, the output of the high-frequency power source wasadjusted within the range of 0.28 to 1.1 W/cm² while the concentrationof CF₄ gas was fixed at 1%. Each case made it possible to form a diamondproduct whose Surface state was favorable, whereas its alignedprotrusions had a substantially perpendicular side face with an angle ofinclination α of at least 78°. In the case where an electric power of atleast 0.45 W/cm² was supplied between the plate electrodes, as can beseen when Examples 7 and 8 are compared with each other, subsidiaryprotrusions were eliminated, and it was possible to greatly increase theangle of inclination α.

While the invention achieved by the inventors is specifically explainedwith reference to the embodiments and examples in the foregoing, thepresent invention should not be limited to the above-mentionedembodiments and examples. For example, the aligned protrusions may beformed not only into a matrix, but also into a triangle, a hexagon, andthe like as long as they are arranged with a predetermined regularity.The mask layer may be formed not only from Al, but also from materialsresistant to oxidization such as Al₂O₃, AlN_(x), SiO₂, and Si. Also, theform of aligned protrusions and depressions (recesses) can be changedfreely when the form of mask layer is changed. Further, the etching forforming the diamond product may be ECR etching, etching by ICP, or thelike without being restricted to the reactive ion etching.

As explained in the foregoing, the present invention can sufficientlyflatten the surface of a diamond product, and make etched side facessubstantially perpendicular.

From the invention thus described, it will be obvious that theembodiments of the invention may be varied in many ways. Such variationsare not to be regarded as a departure from the spirit and scope of theinvention, and all such modifications as would be obvious to one skilledin the art are intended for inclusion within the scope of the followingclaims.

1. A method of making a diamond product by etching, said methodcomprising the steps of: forming a diamond substrate with a mask layer;and etching said diamond substrate formed with said mask layer with aplasma of a mixed gas composed of a gas containing an oxygen atom and agas containing a fluorine atom; wherein said fluorine atom has aconcentration within the range of 0.04% to 6% with respect to the totalnumber of atoms in said mixed gas.
 2. A method of making a diamondproduct according to claim 1, wherein said plasma is produced bygenerating a high-frequency discharge between two plate electrodesarranged in parallel; and wherein said high-frequency discharge isgenerated by supplying an electric power of at least 0.45 W/cm² betweensaid plate electrodes.
 3. A method of making a diamond product accordingto claim 1, wherein said gas containing said fluorine atom is CF₄ gas;and wherein said CF₄ gas has a concentration within the range of 0.02%to 3% with respect to the total number of molecules in said mixed gas.4. A method of making a diamond product according to claim 1, whereinsaid gas containing said oxygen atom is one of O₂, CO₂, and a mixed gascomposed of O₂ and CO₂.
 5. A diamond product comprising: a diamondsubstrate; a plurality of aligned protrusions made of diamond, formed onsaid diamond substrate by etching, and arranged according to apredetermined rule; and a plurality of subsidiary protrusions randomlyformed between said plurality of aligned protrusions upon etching;wherein said aligned protrusions have a side face with an angle ofinclination of at least 78°; and wherein said subsidiary protrusionshave a top part which is not flat, the number of said subsidiaryprotrusions being not greater than 20 per 25 μm².
 6. A diamond productcomprising: a diamond substrate having a recess formed by etching; and aplurality of subsidiary protrusions randomly formed at a bottom part ofsaid recess upon etching; wherein said recess has a side face with anangle of inclination of at least 78°; and wherein said subsidiaryprotrusions have a top part which is not flat, the number of saidsubsidiary protrusions being not greater than 20 per 25 μm².
 7. Adiamond product comprising: a diamond substrate; one protrusion made ofdiamond and formed on said diamond substrate by etching; and a pluralityof subsidiary protrusions randomly formed about said one protrusion uponetching; wherein said one protrusion has a side face with an angle ofinclination of at least 78°; and wherein said subsidiary protrusionshaving a top part which is not flat, the number of said subsidiaryprotrusions being not greater than 20 per 25 μm².
 8. A method of makinga diamond product by etching, said method comprising the steps of:forming a diamond substrate with a mask layer; and etching said diamondsubstrate formed with said mask layer with a plasma of a mixed gascomposed of a gas containing an oxygen atom and a gas containing ahalogen atom; wherein, in an emission spectrum of said mixed gas, anintensity A of an emission peak caused by said oxygen atom and anintensity B of an emission peak caused by oxygen have an intensity ratioA/B which is greater than the intensity ratio A/B obtained from anemission of a plasma which is 100% oxygen.
 9. A method of making adiamond product according to claim 8, wherein said gas containing saidhalogen atom is CF₄, and wherein said mixed gas further containsnitrogen gas.
 10. A method of making a diamond product according toclaim 8, wherein said emission peak caused by said oxygen atom has ahalf width of 3 nm or less, and wherein said emission peak caused byoxygen has a half width greater than 3 nm.